Telephone-exchange system



Augf 25; 1925. I 1,551,024

' C. L. GOODRUM TELEPHONE EXCHANGE SYSTEM Filed Dec. 22, 1921 13 $heets-Sheet 1 Ill 'II' I 666% Mrs/77W. Char/e5 A. Goad/um,

Aug; 25. 1925. 1,551,024

' C. L. GOQDRUM TELEPHONE EXCHANGE SYSTEM Filed Dec. 22, 1921 15 Sheets-Sheet 2 llll Aug. 1:), 192:). 1,551,024

c. L. GOODRUM TELEPHONE EXCHANGE SYSTEM Filed Dec. 22, 1921 13 Sheets-$heet 5 awn/w? Char/e5 A. @ooah/m,

Aug. an, 1925. 1,551,,Q24

. C. L. GQODRUM TELEPHONE EXCHANGE SYSTEM Filed Dec. 22, 1921 13 Sheets-sh et 2* Char/65 L Good/0m,

k I y 4 7 Aug. 25, 1925. 1,551,024 I c. L. GOODRUM TELEPHONE EXCHANGE SYSTEM Filed Dec. 22, 1921 13 Sheets-Sheet 5 Aug. 25, 1925. 1,551,924

C. L. GOODRUM TELEPHONE EXCHANGE SYSTEM Filed Dec. 22. 1921 13 Sheets-Sheet 6 Aug. 25, 1925.

0. L. GQODRUM TELEPHONE EXCHANGE SYSTEM Filed Dec. 22, 1921 13 sheets-sheet: 'r

lave/77am Char/9s LGooarum y ny Aug. 25. 1925.

' 1,551,024 c. L. GOODRUM TELEPHONE EXCHANGE SYSTE M .Filed Dec. 22, 1921 '13 sheets-sheet a Aug. 25, 1925. 1,551,024

c. L. GOODRUM TELEPHONE EXCHANGE SYSTEM Filed Dec. 22, 1921 13 Sheets-Sheet 9 Aug. 25, 1925 1,551,024

c. L. GOODRUM TELEPHONE EXCHANGE SYSTEM Filed Dec. 22, 1921 13 Sheets-Sheet 10' Wye/77W. C/iar/as Z 6004mm,

Aug. 25. 1925 -c. L. GOODRUM TELEPHONE EXCHANGE SYSTEM Filed Dec 22 1921 13 h t g n //7 1/677 70/ Char/e5 A. 6004mm,

T EMM Aug. 25, 1925.

1,551,.024 c. L-. GOQDRUM TELEPHQNB EXCHANGE SYSTEM Fild 1590.22, 1921 13 Sheets-5heet 2.

(724M515 1. 6204mm Aug. 25, 1925. 1,551,024

C. L. GOODRUM TELEPHONE EXCHANGE SYSTEM Filed Dec. 1921 13 Sheezs5heet 1;.

Cfiar/ej L. Goad u PATENT OFFICE.

GHARLES L. GOODRUM, OF NEW YORK, N. Y., ASSIGNOR T0 WESTERN ELECTRIC GOM- PANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Application filed. December 22, 1921. Serial No. 524,083.

To all whom it may concern:

Be it known that I, CHARLES L. GoonRUM, a citizen of the United States, residing at New York, in the county of New York, State of New York, have invented certain new and useful Improvements in Telephone- Exchange Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to telephone exchange systems.

The objects of the invention are simplicity of construction, positive action, speedy operation, low first cost, low maintenance charges and flexibility in the arrangement and size of line and trunk groups.

Switching devices having simple movements of slight extent are incorporated in a system of trunking wherein straight for-- ward selection is practiced, where trunk hunting is limited, and where the controlling apparatus is reduced to a minimum through the use of common senders.

A feature of the invention is the adaptation of common senders to trunk lines, each having a plurality of points of egress. Trunk lines of this general character have heretofore necessarily included individual controlling apparatus. By here employing common apparatus, the first cost of the system is greatly reduced, and maintenance is lowered.

Another feature of the invention resides in the adaptation of a marker for identifying the trunk line at any one of its points of egress. The marker is common to the senders which in turn are common to the trunk lines, and the multiplication of elements is thus reduced. Facility of connection is obtained by the use of what may be termed three coordinate selection, each trunk line terminating as it does in a plurality of points of egress and a non-numerical switch being located at each of these points of egress. The line is extended by identifying the particular trunk line at a particular point in one of its points of egress through this three coordinate selection. The first selection is of the particular point of egress; the second selection is of the trunk line in one of the two principal directions of a two coordinate system within the particular point of egress; and the third selection is of a second principal direction of such two coordinate system. The first coordinate selection is made directly in response to the setting of the sender, and the second and third coordinate selections are made in accordance with the manner in which the trunk line has gained access to the sender, all three selections being controlled directly by the marker.

Another feature of the invention resides in the novel method of operation whereby after the selection at any stage is made the connecting apparatus is not operated until controlling apparatus for the next selection stage is seized and made ready for use.

A further feature resides in the provision in a system of the character herein described of a multi-group connector with means for identifying the proper group in accordance with the character of the digit used in selecting the connector, the selection being determined by the value of the digit.

Another feature resides in the provision of a system employing selective switches comprising a plurality of link circuits for interconnecting incoming and outgoing lines together with sets of cooperating bars for operating said switches, and means consisting of recording devices for governing the operation of said switches.

The drawings placed together as indicated in Fig. 14. illust'ate in a complete diagrammatic form a telephone system involving the invention. Fig. 1 represents a group of lines with non-numerical or line switch mechanism for connecting the lines When calling to trunks leading to the main groups of lines in the exchange. The system to be described has a capacity of ten thousand lines and straight forward selection is provided for. Each line may, therefore, be designated by four digits. The outgoing trunks from Fig. 1 lead to mechanism serving the main groups'or the different thousands groups and lines. Fig. 2 represents a non-numerical switching mechanism which may be selected in response to the sending of the first digit and the apparatus of this figure therefore represents the first group selecting stage. The trunk lines leading from Fig. 1 to Fig. 2 therefore lead in the direction of the main groups of lines and the operation of the switching apparatus of Fig. 2 directs the traffic through such trunk lines to a particular one of said main groups of lines. Fig. 3 in the same manner represents a second group selecting stage and Fig. 4 represents the third. group selecting stage and the fourth or line selecting stage and corresponds to the final selector stage in modern automatic telephone systems.

Fig. 5 represents a sender selector, in other words, a non-numerical switching mechanism for connecting the trunks leading from the line switch mechanism of Fig. 1 to the sender which is diagrammatically shown in Fig. 6 so that upon the initiation of a call from one of the lines of Fig. 1, such line will be extended through the line switch of Fig. 1, and the sender selector of Fig. 5 to the sender of Fig. 6. Fig. 6 also includes an associated marker shown in the righthand portion of the figure for identifying the trunk at any one of its points of egress of which the switching mechanism of Fig. 2 is one.

Figs. 7 and 8 are practically the same as Figs. 5 and 6 and perform the same functions in relation to the mechanism of Fig. 3, as the apparatus at Figs. 5 and 6 perform for the circuits of Fig. 2. Figs. 9 and 10 represent a sender selector and a sender and marker, respectively, for the final selector of Fig. 4 and correspond very closely to the circuits of Figs. 7 and 8. Fig. 11 illustrates the circuits of apparatus of the trunks between the second group selecting stage and the final selector which functions after the called line has been selected to either return the busy tone to the calling subscriber in case the called line is found to be busy or to ring the called subscriber and complete the connection in case his line is found to be idle. Fig. 12 is a general trunking arrangement and diagrammatically illustrates the interconnection of trunks each of which may be reached through a single switch structure and has a plurality of points of egress. Fig. 13 is a perspective of the mechanical apparatus which may be employed in the circuits and which is shown as a coordinate switch.

Gemcml description.

Rectangle 1202 in Fig. 12 represents the connecting mechanism into which lines 0 to 99 enter, and out of which trunks, which for convenience we will number 0 to 9 lead. In a similar manner rectangle 1203 represents the connecting mechanism into which lines 100 to 199 enter and from which trunks 10 to 19 lead. In a fully equipped system of a decimal and 10 per cent trunking basis, there will be ten of these groups of mechanisms serving lines 0 to 999, inclusive, and out of which trunks 0 to 99 lead. Trunks 0 to 99 then go into connecting mechanisms in the same manner as the separate groups of calling lines. For instance, rectangle 1204 represents connecting mechanism into which trunks 0 to 99 enter, and out of which trunks, which for convenience are numbered 1000 to 1009, lead. These trunks 0 to 99 also enter nine other connecting mechanisms represented here by rectangles 1205, 1206, etc. Thus, a trunk such as one of the trunks 0 to 9 has a single switch structure for i11- gress at 1202 and a plurality of points of egress as at 1204, 1205, 1206, etc. A point of ingress is that point of the trunk into which trafiic flows, and the point of egress is that point out of which the traffic flows. Thus the connection being established from the group of lines 0 to 99 will be connected to one of the trunks 0 to 9 at its single point of ingress 1202 and thence extended through one of its points of egress such as 1204.

The calling subscriber in the group 100 to 199 upon initiating a call is connected to a trunk in group 10 to 19. If this calling subscriber desires connection to a subscriber in the first thousands group he will manipulate his calling device to identify the trunk in that one of the ten mechanisms into which this trunk enters which will extend the line to the main group of lines numbered 1000 to 1999. e will assume that rectangle 1204 is the desired one and that by sending one impulse he may identify the trunk to which he has been connected in the group 1204 and thereby select a trunk group 1000 to 1009. There are ten such mechanisms as 1204 into which the trunks of the calling subscribers enter and out of which trunks 1000 to 1099 lead. The trunks 1000 to 1099 each enter ten mechanisms similar to 1204, two of which are here shown as No. 1207 and No. 1215. The subscriber having picked out a line in the first thousands group now wishes to select a line in the first hundreds group of the first thousands group by selecting the first mechanism 1207. By sending one impulse he is then connected to one of the group of trunks represented by 1208. This trunk leads into a connecting mechanism 1214 serving lines 1100 to 1299. By now manipulating his sending device in accordance with the last two digits of the called subscribers number, he will cause his line to be connected through the mechanism 1214 to the particular called line in the group 1100 to 1299.

The particular type of non-nun'ierical switching mechanism used in this disclosure lends itself readily to large groups and as an illustration the connecting device corresponding to the final selector has been shown as a 200 line mechanism. The switching device of Fig. 3 representing the second group selecting stage will automatically differentiate between the even and odd digits so that if the calling subscriber had dialed two in the second instance, and had his con nection extended through the switching device 1215 instead of through the switching device of 1207, he would still be directed into the final selecting device 1214, but the switching device 1215 having been selected through the use of an even number of impulses would identify the connection properly in the 200 line switching device 1214. In the manipulation of the dial in accordance with the last two digits, the line in the group 1200 to 1299 will be selected.

For convenience, the general aspects of the trunking scheme have been shown in Fig. 12 in a. purely decimal and 10 per cent system. The switching device employed, however, readily lends itseli to larger group working and hence it is not at all necessary to lead 100 lines into a group and ten trunlr out of the group, but the relationship between the trunks and the lines may be varied according to the demands of tra'liic in that particular group.

In Fig. 1 there are shown six lines in two groups to represent the grouping arrangement in a non-numerical switch similar in function to the well known line switch. The switch contacts of the lines may be coordinately arranged in horizontally and vertically extended groups. The lines of each horizontally extending group may have the same units digit but a different tens digit. The contacts of lines having the same tens digit but different units digits would then be grouped one above the other. In each such vertical group all switch contacts are under the control of the same magnet such as 104. The line relays control primarily the operation of all the switch magnets and the connections from the relays to the magnets may be varied according to any desired plan so that it is not at all necessary that the lines should be numbered or arranged in the manner stated. The arrangement described, however, is typical and is given for the sake of convenience and illustration.

A. calling line is identified by two magnets, one having control over the group in one coordinate direction and the other magnet having control over the group in the other coordinate direction. When a line, therefore, initiates a call and causes its line relay to be energized, this line relay will in turn cause the energization of those two mognets representing the intersection of the two ooordinates defining this line. A switch of this character is shown in Fig. 13 and functions as follows:

Assume that it is desired to establish a connection between the group of conductors 1, 2, 3 and 4 and the group of conductors 5, 6, '7 and 8. Conductor 5 is multipled at several points to spring wires such as 9 and 10; conductor 6 is multipled in the same manner tospring wires 11 and 12; conductor 7 is multipled to spring wires 13 and 14, and conductor 8 is multipled to spring wires 15 and 16.

Associated with the group 01": conductors 5, 6, 7 and 8 is a magnet 104 which controls an armature 18 to rotate a bar or switching member 19. Secured to this bar and associated with each group of spring wires such as 9, 11, 13 and 15 and 10, 12, 14 and 16, are spring wires 20 and 21, respectively. When the magnet 104 is energized all of the spring wires such as 20 and 21 are moved in a clockwise direction through the rotation of bar 19.

Associated with the group of conductors 1, 2, 3 and 4 is a magnet 168 which, through an armature 23, controls a switching member or bar 24. Secured to this bar and associated with each group of conductors similar to the group 5, 6, 7 and 6 are arms such as 25 and 26. After the magnet 104 has become operated and the spring wire 21 has moved to a position above the arm 26, the magnet 168 may be operated whereupon the spring wire 21 will be moved upwardly. Each of the arms such as 25 and 26 contains a notch 27 which is for the purposeof preventing the spring wire 21 from slipping when the magnet 104 is deenergized to return all of the spring wires such as 20 back to their normal positions, leaving only the one 21, in an operated position.

Associated with each group of spring wires such as the group 9, 11, 13 and 15 and the group 10, 12, 14 and 16, is a piece of insulating material such hard rubber or fiber 110 and 109. The spring wires 10, 12, 14 and 16 project through slots cut in the insulating material 109. This insulating piece is so fastened at its lower end that when the spring 21 has been moved in a clockwise direction and the arm 26 has been rotated upwardly, spring 21 will move the insulating piece 109 bodily upward, bringing the spring wires 10, 12, 14 and 16 into contact with conductors 1, 2, 3 and 4, respectively.

For holding the piece of insulating material 109 in position, two springs 30 and 31 are provided which are threaded through the insulating material and bent over in a manner to locate the piece 109. The spring wire 31 after being threaded through the insulation is also bent upwardly and then outwardly so that when the group of spring wires 10, 12, 14 and 16 is at rest, they will be prevented from moving downwardly a sutlicient distance to contact with the conductors of the group 1, 2, 3 and 4.

It will be seen from this arrangement that if two magnets 104 and 112 are simultaneously energized and then magnet 168 is ener gized, -a connection will be established from conductor 5 to conductor 1 and thence to conductor 33 and in the same manner conductors 6, 7 and 8 will be connected through conductors 2, 3 and 4 to conductors 34, and 36.

The lines of Fig. 1 are assumed to be in lit the zero thousand group of lines, and for convenience in illustrating, the manner in which the various senders are operated, the group of called lines in Fig. 4 is assumed to be in the 1400 group of lines. For the purpose of fully disclosing the present invention, a connection established by the subscriber on line 0011 to called line 1427 will be described. Such a connection niay be traced from the non-munerical switch of Fig. 1, where by means of switching devices 107 and 113, it is connected to trunk 11%). Such a trunk line appears in the one non numerical switch of Fig. 1 and has a plurality of points of egress in switching mechanisms such as is shown in Fig. 2, and which are reached through the multiple taps 222.

The device herein termed a marker employs a multiple contact relay such as that shown, described and claimed in the copencling application of Forsberg, Serial No. 482,106, filed July 2, 1921. This marker is shown in the right-hand portion of Fig. 6, and functions to identity the particular trunk employed in one of the plurality of points of egress, and thus forms a means for manipulating what may be termed a three-coordinate system. The selection of a particular row of contacts by either magnet 610, 611, 612, etc., determines the first coordinate selection. The selection of a particular magnet 606, 607, etc. determines the second coordinate selection and the selection of particular contacts in the row selected by these magnets, as determined by the manipulation of the counting relays of the sender, determines the third coordinate selection. By means of these three coordinate selections the trunk 118 may be identified in any one of its points 01" egress, and its identification in the switching mechanism of Fig. 2 will be hereinafter fully described.

When the subscriber at station 100 on line 0011 removes his receiver from its switchhoolr, line relay 102 will be energized. This will immediately cause the fill'l flZw tion of magnet 104 and magnet 104 will in turn cause the energization of magnet 112, which will prepare for operation, the switching devices shown vertically a iove them. The energization o1"- magnet 112 will result in the energization of two siniiila-r magnets in the sender selector of Fig. 5, namely, magnets 504 and 512. These two magnets likewise prepare for operation the switching devices shown vertically above them. Upon the operation of magnet 512, the impulse relay of the sender and there after the holding relay of the sender, are energized, whereupon the magnet 50.3 will become energized and operate two of the switching devices prepared for operation by magnets 504 and 512. These switching devices are numbered on the drawings 509 and 515, respectively. Through the operation of the holding relay of the sender, magnet- 503 will be locked in its energized position. lVhen the switching devices 515 and 509 have been operated, a ground connection from the holding relay of the sender will be extended back over the trunk 118, whereupon the magnet 103 will become energized and operate the switching devices 107 and 113. Thus it will be seen that the complete 0 )erat-ion of the switching device of Fig. 1 depends upon the successful connection of a sender to the trunk which will be used. It no sender is available at this time, the three magnets 104, 112 and 504 will remain operated under the control of the calling subscribers line relay, and will remain in this condition until a. sender becomes available and is seized through the energization of the magnet such as 512. This feature of delaying the action of the switching mechanism at any one of the selecting stages until a sender is actually available and connected to the trunk will be observed throughout the following detailed description of the operation. When the sender of Fig. 6 is seized and the holding relay thereat is operated, the. ground connection will be extended back over trunk 1.18 as described to cause the operation of magnet 103. Magnet 103 will lock to the ground connection controlled by the holding relay oi the sender. Upon the operation of this magnet, magnets 104 and 112 will be deenergized, and in turn magnets 504 and 512 will be deenergized. The subscribers line 0011 is now extended to the sender and has control over the counting relays so that upon the manipulation of the impulse transmitter at substation 100, the sender will be operated.

The connector switch shown in Fig. 4 is designed with a 200-line capacity, the subscribers lines terminating therein being divided for that purpose into ten groups of twenty lines each, each group of twenty lines being further divided into two sections of ten lines each. All lines in the group of 200 having the same units digit are grouped in one subgroup oftwenty lines. Thus, as shown, lines 1417, 1427, 1437, etc. having the units digit 7 comprise one subgroup in one coordinate direction and likewise lines 1416, 1426, 1436, etc. having the units digit 6 comprise another similar sub group. Selection of subgroups in the units coordinate direction is ell'ected through the selection and operation of a units magnet such as 403 under the control of the units contacts of either one of the markers 1006 or 1007 in Fig. 10.

Tens selection in the other coordinate direction of the connector switch is eflected through the selection and operation of tens magnets such as shown at 404, 405 and 406.

Since each subgroup of lines comprises twenty lines, two sections of ten magnets each are provided. Each units subgroup of lines thus includes lines having the same units and tens digit but different hundreds digits. Thus, under the assumption that the connector switch, Fig. 4, serves the group of lines including lines 1300 to 1499, inclusive, the subgroup having the units digit 7 would include lines 1317, 1327, 1337, etc., as well as lines 1417, 1427, 1437, etc. It is thus necessary to further divide each units subgroup of twenty lines in the other coordinate direction of the switch into two sec tions as hereinbefore noted, the sections being characterized by the hundreds digits, being odd or even, lines 1317, 1327, 1337 thus constituting one such section and lines 1417, 1427 and 1437 the other section. Magnet 404 then serves in the selection of all lines having the even hundreds digit 4 and the tens digit 1, and similarly magnet 405 serves in the selection of all lines having the even hundreds digit 4 and the tens digit 2. For the selection of lines having the odd hundreds digit 3 and tens digits 1 to 0, inclusive, a second set of magnets similar to magnets 404, 405 and 406 is provided.

When the hundreds digit glS even, the marker 1007 is operated and marks a units magnet such as 403 and a tens magnet of the even hundreds section such as 404, 405 or 406 for subsequent operation. If the hundreds digit odd the marker 1006 is operated and marks a units magnet and a tens magnet of the odd hundreds section (not shown) over conductors such as 1076, 1077 and 1078 of Fig. 10 for subsequent operation.

Having thus given a general description of the action of the apparatus in response to the initiation of a call, the circuits will be described in detail.

Detail description of circuit operation.

When the subscriber at station 100 removes his receiver from the switchhook, a circuit will be established from battery, right-hand winding of line relay 102, back contact and inner left-hand armature of cutofl relay 101, over the loop of the calling substation 100 the outer left-hand armature and back contact of cutoff relay 101, the left-hand winding of line relay 102 toground. Line relay 102 becomes energized in this circuit and establishes the following connection for the energization of magnet 104: from ground, left-hand armature and back contact of magnet 103, conductor 150, front contact and inner armature of line relay 102, con ductor 151, winding of magnet 104 to battery. ltlagnet 104 becomes energized and prepares for operation switching devices 107 to 110, inclusive. Upon its energization, magnet 104 removes the battery connection from magnets 105 to 106 so as to prevent the possibility of a double connection. A circuit is also established at this time from ground, the inner right-hand armature and front contact of magnet 104, conductor 152, armature and front contact of relay 119 (assuming trunk 117 to be busy at this time) armature and back contact of relay 120, winding of magnet 112 to battery (assuming trunk 118 to be idle at this time).

Magnet 112 becoming energized, prepares for operation switching devices 113 to 116, inclusive. A circuit is now established from ground, the left-hand armature and front contact of magnet 112, conductor 153, conductor 250, conductor 550, Winding of magnet 504, to battery and ground. Magnet 504 prepares for operation switching devices 507 to 510, inclusive, and removes the battery connection from the windings of magnets 505 and 506 to prevent the possibility of a double connection. A circuit is now established from ground, the front contact and left-hand armature of magnet 504, conductor 552, armature and front contact of relay 519, (assuming trunk 517 to be busy at this time) armature and back contact of relay 520, winding of magnet 512 to battery and ground. Magnet 512 becomes energized in this circuit and prepares for operation switching devices 513 to 516, inclusive. Upon its energization magnet 5-12 establishes a connection from ground, lefthand armature and first front contact, conductor 553, conductor 554, conductor 254, conductor 154, inner right-hand armature and front contact of magnet 112, conductor 155, conductor 255, conductor 555, normal contacts of the inner armature of magnet 503, winding of magnet 503 to battery and ground. Magnet 503 becomes energized in this circuit and operates switching devices 509 and 515. Through the energization of magnet 512 a circuiit is also established from ground, left-hand armature and second front contact of magnet 512, conductor 551, conductor 600, winding of impulse relay 601, to battery and ground. Relay 601 becomes energized in this circuit and establishes a circuit from ground, armature and front contact of relay 601, winding of slow-torelease holding relay 603 to battery. Holding relay 603 attracts its armatures and establishes a connection from ground, lefthand armature and front contact of relay 603, conductor 604, conductor 556, through the corresponding contacts of switching device 515, conductor 557, inner armature and alternate contact of magnet 503, winding of magnet 503, to battery, whereby magnet 503 remains locked in its energized position. Grounded conductor 557 is also connected through the corresponding contacts of switching device 509 to conductor 558, conductor 253, normal contacts of the right-hand armature of relay 201, conductor 251, conductor 156, outer right-hand armature and front contact of magnet 112, conductor 157, lefthand armature and front contact of magnet 104, conductor 158, outer armature and front contact of line relay 102, conductor 159, normal contacts of the inner right-hand armature of magnet 103, winding of magnet 103, to battery and ground. Magnet 103 becomes energized in this circuit and causes the operation of switching devices 107 and 113, whereupon grounded conductor 156 is connected through the corresponding contacts of switching device 113 toconductor 160 and thence through the inner right-hand armature and alternate contact of magnet 103, winding of magnet 103 to battery and ground, to maintain this magnet locked in its energized position. Grounded conductor 160 is also extended through the correspending contacts of switching device 107 to conductor 161, and thence through the winding of cutofi relay 101, which becomes energized and cuts off the line relay from the control by the substation 100. The ground potential on conductor 161 is also extended through the corresponding multiple tap in the group 122 to mark this line as busy in the connector switch in which it appears, the taps 122 being connected to corresponding taps in the proper hundreds group connector.

Through the operation of magnet 103 and cutoii" relay 101, the original energizing circuitfor magnet 104 is opened, and this magnet becomes deenergized. Thereupon, the energizing circuit for magnet 112 is opened, and this magnet in turn becomes deenergized. Upon its deenergization, grounded conductor 156 is connected through the outer right-hand armature and back contact of magnet 112, through the winding of relay 120 to battery, so that the starter wire 152 may be extended to the next idle trunk. The deenergization of magnet 112 opens the original energizing circuits for magnets 504 and 503. Magnet 504 becomes deenergized, but magnet 503 remains operated due to the locking circuit which has been established. Upon the deenergization of magnet 504, the original energizing circuit for magnet 512 is opened and it becomes deenergized. Upon the retraction of the armatures of magnet 512, the original energizing circuit for the impulse relay 601 is opened, but a substitute circuit has previously been established which may be traced from battery, winding of impulse relay 601, conductor 600, conductor 551, corresponding contacts of switching device 515, conductor 559, corresponding contacts of switching device 509, conductor 560, conductor 260, outer left-hand armature and back contact of relay 201, conductor 253, conductor 162, corresponding contacts of switching device 113, conductor 163, corresponding contacts of switching device 107, conductor 164, through the loop substation 100, conductor 165, corresponding contacts of switching device 107, conductor 166, corresponding contacts of switching device 113, conductor 167, conductor 256, back contact and inner left-hand armature of relay 201 to ground. Through this circuit the subscriber at station 100 has complete control over the sender of Fig. 6. Also, through the deenergization of magnet 512 the grounded conductor 556 is connected through the right-hand armature and back contact of magnet 512, the winding of relay 520, to battery and ground, whereupon this relay becomes energized and extends the starter wire 552 to the next idle trunk.

All of this operation has taken but a fraction of a second and the apparatus which has responded to the initiation of the call at substation 100 is now in a stable condition awaiting the manipulation of the impulse transmitter.

It should be noted at this point that if another call should now be initiated, say by line 0012, that magnet 104 will again be operated, but will in no way aflfect the switching device 107 since this is locked against operation by the magnet 103. At this time switching devices 108, 109 and 110 will be prepared for operation, and when the rest of the apparatus is in condition, magnet 169 will become energized (assuming that magnet 168 is energized in a connection extending line 0022 over the link 170 to trunk 117). The energization of magnet 169 in the present case will extend line 0012 over link 171 to the next idle trunk similar to trunks 117 and 118. It will thus be seen that every idle link circuit, such as 121, 170 and 171, is available, and very little apparatus other than that actually used in the connection is rendered incapable of use during the existence of a connection. It is to be particularly noted that a magnet such as 104 may be used to successively establish a plurality of connections.

Thousands selection.

Through the use of the sender selector and the non-numerical switch of Fig. 1, a small number of senders, only so many as the tratfic requires, may be made common to a large number of calling lines. Fig. 6 represents two such senders, the broken line rectangle to the left being a duplicate of the organization of relays forming the sender which is located in the center of this figure. Since it has been assumed that the number of the called substation is to be 1427, the subscriber on line 0011 will manipulate his impulse sending device (not shown) at substation 100 to send a single impulse. Such an impulse is in the form of a single short interruption of the subscribers line circuit, and controls impulse relay 601 by causing it to retract its armature for an instant. During the retraction of this armature, the energizing circuit for holding relay 603 is opened, but this relay being of the slow releasing ,type, ,does not respond. Therefore a circuit is established from ground, armature and back contact of impulse relay 601, right-hand armature and front contact of holding relay 603, winding of relay 603 to battery and ground, and in parallel with the winding of relay 608, through the lower armature and back contact of relay 609, winding of relay 613 to battery and ground. Relays 603 and 613 respond to the establishment of this connection and attract their arn'iatures. Relay 613 thereupon establishes a circuit from ground, the left-hand armature and front contact of relay 603, conductor 60%, front contact and upper armature of relay 613, winding of relay 609, winding of relay 613 to battery and ground. Relay 609, however, does not become energized at this time due to the ground connection from its own lower armature and front contact to the connection between the windings of relays 609 and 613. At the end of the interruption of the circuit of relay 601, the armature of relay 601. is again attracted and the original circuit for the energization of relay 613 is broken, but now the substitute circuit through the winding of relay 609becomes effective and relay 609 also becomes energized. Succeeding impulses would in a similar manner cause the energization of successive pairs of counting relays 617, 628, etc., there being ten pairs of such relays provided for each sender. Relay 606, being of the slow releasing type, does not immediately become deenergized, so that if more impulse. were to be sent, this relay would remain energized until after the final impulse had been. recorded. There being but one impulse in this train, relay 608 now becomes deenergized, whereupon a ci *cuit is established from ground, armature and front contact of relay 601, front contact and outermost upper armature of relay 609, a-rniiature and back contact of relay 608, winding of relay 61 1, to battery. Through its innermost leit-hand armature, relay 614 cuts off the battery connection to similar relays in other senders corresponding to that shown in the sender of Fig. 6, one of which is designated 620 in the broken line rectangle at the left of Fig. 6. Relay 614 now establishes a circuit from ground, inner rigl'it-hand armature and front contact of relay 6141-, conductor 615, conductor 561, corresponding contacts of switching device 515, conductor 562, cor responding contacts of switching device 509, conductor 563, conductor 616, magnet 610, to battery and ground. Through the energization of magnet 610 a circuit is established from ground, front contact and middle left-hand armature of relay 61 1, inner upper armature and front contact of relay 609, upper armature and back contact of relay 617, conductor 618, corresponding contacts of switching device 619 (controlled by magnet 610), conductor 621, conductor 56%, conductor 257, winding of magnet 2041, to battery and ground. Magnet 204; becomes energized in this circuit and prepares for operation switching devices 207 to 210, inelusive. Upon its energization magnet 204: establishes a connection from ground, front contact and left-hand armature of magnet 20%, conductor 258, armature and front contact of relay 219, (assuming that trunk 217 is at the time busy), the armature and back contact of relay 220, (assuming trunk 218 to be idle at this time), winding of magnet 212, to battery and ground. Magnet 212 becomes energized in this circuit and prepares for operation switching devices 213 to 216, inclusive. Upon its energization magnet 212 establishes a connection from ground, left-hand armature and front contact of magnet 212, conductor 259, conductor 350, conductor 750, winding of magnet 7 04, to battery and groimd. Magnet 704. becomes energized in this circuit and prepares for operation switching devices 707, 708, 709 and 710. A circuit is now established from ground, front contact and left-hand armature of magnet 704:, conductor 752, armature and front contact of relay 719, (assuming trunk 717 to be busy at this time), armature and back contact of relay 720, winding of magnet 712 to battery and ground (assuming trunk 718 to be idle at this time), Magnet 712 becomes energized in this circuit and prepares for operation switching devices 713, 71 1-, 715 and 716. Magnet 712 also establishes a circuit from ground, lefthand armature and first front contact, conductor 753, conductor 754, conductor 354, conductor 260, inner right-hand armature and front contact of magnet 212, conductor 261, conductor 355, conductor 755, normal contacts of the inner armature of magnet 703, winding of magnet 703 to battery and ground. Magnet 703 becomes energized in this circuit. A circuit is also established from ground, left-hand armature and second front contact of magnet 712, conductor 751, conductor 300, winding of impulse relay 801 to battery and ground. Impulse relay 301 becomes energized in this circuit and attracts its armature establishing a circuit for slow releasing holding relay 803 over a circuit including ground, armature and front contact of relay 801, conductor 802, winding of relay 803 to battery and ground. Relay 803 in attracting its armatures establishes a circuit from ground, left-hand armature and front contact of relay 803, con- 

